1. Field of the Invention
The present invention relates to a honeycomb filter and an exhaust gas purifying system.
2. Discussion of the Background
In recent years, particulate matter (hereinafter, also referred to as “PM”) such as soot contained in exhaust gases discharged from internal combustion engines of vehicles such as buses and trucks, construction machines and the like have raised serious problems as contaminants harmful to the environment and the human body. For this reason, various honeycomb filters, which use a honeycomb structured body made of porous ceramics, have been proposed as filters that capture PM in exhaust gases and purify the exhaust gases.
In a honeycomb filter of this kind, a catalyst used for purifying and/or converting exhaust gases may be supported thereon, and in this case, a catalyst supporting layer is formed in an area on which the catalyst is to be supported, so that the catalyst is supported on the catalyst supporting layer.
JP-A 2003-154223 has disclosed a honeycomb filter made from silicon carbide, in which a higher amount of catalyst is supported on the side that allows exhaust gases to flow in (gas inlet side) and a lesser amount of catalyst is supported on the side that allows exhaust gases to flow out (gas outlet side), or a catalyst is supported only on the gas inlet side and substantially no catalyst is supported on the gas outlet side; and an exhaust gas purifying system in which the honeycomb filter of this kind is placed in an exhaust gas passage.
JP-A 2003-161138 has disclosed a honeycomb filter that is designed to make the amount of supported catalyst successively smaller step by step or continuously, from the gas inlet side toward the gas outlet side of the honeycomb filter.
The contents of JP-A 2003-154223 and JP-A 2003-161138 are incorporated herein by reference in their entirety.